This invention relates to an industrial detergent in the form of aqueous solution, which contains organic surface-active agents and is useful for cleansing metal parts.
In general, metal parts produced by machining or plastic working such as press-forming must be subjected to a degreasing and cleansing process preparatory to a surface treatment process such as plating, painting or electrochemical rust-inhibiting treatment. A prevailing method for industrial degreasing and cleansing of metal parts is to use an alkaline detergent, though other methods such as cleansing with an acid or an organic solvent and removal of grease and dirt by combustion are also in practice.
Conventional alkaline detergents for this use are usually in the form of aqueous solution containing inorganic surfactants and builders such as caustic alkali, alkali phosphate, lime, alkali carbonate and/or alkali silicate and having pH values above about 9.5. Due to the strong alkalinity, splashing of these detergent solutions is hazardous to the workers and therefore the use of these detergents offers a serious problem to the labor safety and labor environment hygiene. Furthermore, the waste waters treatment is difficult and, even after treatment, can hardly be reused because of high contents of various inorganic salts. Of course, the inorganic ingredients of the alkaline detergents cannot be decomposed by microorganisms in natural water. Particularly, phosphates used as highly effective builders in the alkaline detergents are now regarded as a major source of water pollution because they promote eutrophication of streams, lakes and coastal sea waters and therefore must be eliminated by all means.
Current detergents in a broad sense include synthetic detergents containing organic surface-active agents and having relatively low pH values, but until now such synthetic detergents have been limited to household uses as kitchen cleaners, toilet soaps, shampoos and laundry detergents. The objects of cleaning by the household detergents such as clothing made of fibers and tableware made of ceramic or a stabilized metal such as stainless steel are greatly different from metal parts as machined or press-formed. Also, the dirts and stains to be removed by the household detergents are quite different from grease, machine oil and lubricating oil adhering to the industrially produced metal parts. Accordingly it is no wonder that conventional household detergents do not serve as industrial detergents for metal parts.
The primary requirements of industrial detergents of the class herein concerned with are greatly different from the requirements of household detergents. Considering that the surfaces of metal parts just worked are so active in the electrochemical sense that ionic adsorption constitutes an important factor in the adhesion of dirty matter to the metal surfaces, the detergents must exhibit a sequestering ability. Also considering that the metal surfaces are high in chemical reactivity, the detergents should have a rust- and corrosion-inhibiting ability. Furthermore, the industrial detergents are required to be low in foaming tendency because cleansing of the metal parts is usually performed by a high-temperature high-pressure spraying method in order to complete degreasing and cleansing in a very short period of time.
Until now it has been a common-sense view that the use of strongly alkaline inorganic builders is indispensable to obtain an industrial detergent composition that is sufficiently high in the deterging power, stable at high temperatures and high pressures required to spraying operations, having a chelating effect on metal ions, having rust- and corrsion-inhibiting ability, and weak in foaming tendency.